KAGRA Logbook

memo

The message of ASC_LOCK was 'PRMI seems to be unlocked'. So, the last cause of the lockloss was the failure of 'LSC-POP_PDA2_RF90_I_NORM_MON'] > 0.1.

At -11 s before the lockloss, the DC control was taken over from OLDAMP control to ASC, in INCREASE_SOFTHARD_GAIN state of ASC_LOCK guardian. (Fig)

After that, K1:VIS-ITMX_TM_WIT_Y_DQ seems to start the oscillation and glowing. We can observe the similar trend on K1:ASC-DSOFT_Y_IN1_DQ and K1:LSC-POP_PDA2_RF90_I_ERR_DQ . (right bottom of Fig)

Based on the chat with Kenta-san, this is happening the weak DC control of the ASC during the handover of the ASC and OLDAMP.
The detailed procedure of the takeover will be posted by Kenta-san SOON.

We could see the same trend before the following timing of the lockloss.

2024/09/11 16:02:02 JST (klog) (Fig)
2024/09/11 16:09:05 JST (Fig)
2024/09/11 16:38:00 JST (Fig)
2024-09-11 17:00:36 JST (Fig)
2024-09-11 17:09:45 JST (Fig)

[YamaT, Aso, Tanaka]

Yamamoto-san pointed out that the current order of switching the filters in the MN_OLDAMP bank during the handover from local control to global control may change the alignment. Fig. 1 shows the filter configuration in MN_OLDAMP before the handover. First, the AC filter in FM2 is engaged. Then, the ASC_LOCK guardian opens the input switch of the bank. Finally, the null filter in FM8 is turned on. However, in this order, since the filter DC gain shape become flat at DC after engaging AC filter (fig.2), the DC output changes when the input value become 0 when the input switch is open. Fig.3 shows the test result. We copied the AC, DC, and null filter from MN_OLDAMP to the TEST filter bank. We used the offset instead of the input value. We switched the filter as the same order as the guardian. At the timing on the time kersol in Fig.2, we turned off the offset. As you can see, the DC output value decreased after turning off the input value. This indicates the current switching order changed the alignment during the handover. Therefore we need to turn on the null filter before turing off the input swtich.